Via reactive ion etching process

ABSTRACT

Methods of etching a dielectric layer and a cap layer over a conductor level to open a via to the conductor. The methods include the provision of tetrafluoro methane (CF 4 ) in a photoresist strip. In addition, the methods may provide an increased amount of tetrafluoro methane (CF 4 ) in a dielectric layer etch, and trifluoro methane (CHF 3 ) in a cap layer etch. The invention provides higher yield, more predictable etch rates, faster processing, and removes the need for an ash step.

TECHNICAL FIELD

The present invention relates generally to semiconductor fabrication,and more particularly, to a via reactive ion etching process.

RELATED ART

In the semiconductor industry, reactive ion etching (RIE) is used toopen pathways for circuitry within a semiconductor chip. One structureformed using RIE is a via, which electrically connects conductors withindifferent layers. RIE is a variation of plasma (gas) etching in which asemiconductor wafer is placed on a radio frequency (RF) poweredelectrode, and etching species are extracted and accelerated from theplasma toward the surface to be etched. A chemical etching reactionoccurs which removes parts of the surface. RIE is one of the most commonetching techniques in semiconductor manufacturing.

Referring to FIG. 1, a semiconductor structure 10 including large-viapad dielectric layers 12 prior to etching is shown. Structure 10includes a conductor level 14 including a dielectric layer 16 (e.g., ofsilicon dioxide SiO₂) surrounding conductor 18 (e.g., of copper Cu); acap layer 20 (e.g., of silicon nitride Si₃N₄) atop conductor level 14; adielectric layer 22 (e.g., of silicon dioxide SiO₂); another dielectriclayer 24 (e.g., of silicon nitride Si₃N₄); and a patterned photoresist26. A typical large-via RIE process is conducted in a single plasmachamber capable of two RF settings, e.g., 2 MHz and 27 MHz. Oneconventional RIE process includes the following steps: etching ofdielectric layer 24, etching dielectric layer 22 and stopping on caplayer 20 so as to not expose conductor 18, stripping photoresist 26,etching cap layer 20 to expose conductor 18, and finally, performing anitrogen-hydrogen (N₂H₂) plasma chemistry (ash) to remove residual RIEpolymers from conductor 18. More specifically, dielectric layer 22etching may occur, for example, using the following conditions: 80 mTorr(mT) of pressure, an RF energy of 1800 watts (W) at 27 MHz and 600 W at2 MHz, and a gas flow of 10 standard cubic centimeters per minute (sccm)of tetrafluoro methane (CF₄), 220 sccm of carbon monoxide (CO) and 400sccm of argon (Ar), resulting in an approximately 45 Ångstrom/second(Å/s) etch rate. The photoresist strip may use, for example, thefollowing conditions in two stages including: 800 mT of pressure, an RFenergy of 800 W at 27 MHz, and a gas flow of 1000 sccm of oxygen (O₂),followed by 450 mT of pressure, 1200 W at 27 MHz and 200 W at 2 MHz, anda gas flow including 1000 sccm of oxygen (O₂). The dielectric layer 20etch may occur, for example, using the following conditions: 150 mT ofpressure, an RF energy of 1000 W at 2 MHz and 1500 W at 27 MHz, and agas flow of 100 sccm of oxygen (O₂), 190 sccm tetrafluoro methane (CF₄)and 400 sccm argon (Ar). The ash step may occur, for example, using thefollowing conditions: 200 mT of pressure, an RF energy of 1200 W at 27MHz, and a gas flow including 600 sccm nitrogen (N₂) and 200 sccmhydrogen (H₂).

The conventional RIE process suffers from a number of problems. First,conventional RIE techniques suffer from a low etch rate because the gasflow for the process is typically centered at the minimum operatingrange of a mass flow controller, which reduces yields. Second, typicalplasma processes are susceptible to gas flow fluctuations, e.g., withina process chamber or between different equipment, which results inwidely varying etch rates. Finally, with the movement of waferfabrication facilities from the conventional 200 mm wafer to the larger300 mm wafer, process cycle times of conventional RIE processes areconsidered too long. For example, large via (LV) pads are the finallevel of 300 mm wafer fabrication connecting the transistors to the wirebonds for the final electrical test. The via RIE process for LV padstypically takes approximately 5 minutes per wafer, which makes this stepa target for improvement.

In view of the foregoing, there is a need in the art for an improved viaRIE process that does not suffer from the problems of the related art.

SUMMARY OF THE INVENTION

The invention includes methods of etching a dielectric layer and a caplayer over a conductor level to open a via to the conductor. The methodsinclude the provision of tetrafluoro methane (CF₄) in a photoresiststrip. In addition, the methods may provide an increased amount oftetrafluoro methane (CF₄) in a dielectric layer etch, and trifluoromethane (CHF₃) in a cap layer etch. The invention provides higher yield,more predictable etch rates, faster processing, and removes the need foran ash step.

A first aspect of the invention is directed to a method of etching adielectric layer and a cap layer over a conductor level to open a via tothe conductor, a pattern for the via being provided by a photoresist,the method comprising the steps of: etching the via through thedielectric layer; stripping the photoresist using a plasma chemistryincluding tetrafluoro methane (CF₄); and etching the cap layer to openthe via to the conductor.

A second aspect of the invention includes a method of etching adielectric layer and a cap layer over a conductor level to open a via tothe conductor, a pattern for the via being provided by a photoresist,the method consisting of the steps of: etching the via through thedielectric layer; stripping the photoresist using a plasma chemistryincluding tetrafluoro methane (CF₄); and etching the cap layer to openthe via to the conductor.

A third aspect of the invention relates to a method of etching adielectric layer and a cap layer over a conductor level to open a via tothe conductor, a pattern for the via being provided by a photoresist,the method comprising of the steps of: etching the via through thedielectric layer using approximately 80 mT of pressure, an RF energy ofapproximately 1200 W at 27 MHz and approximately 2700 W at 2 MHz, and agas flow including tetrafluoro methane (CF₄) and carbon monoxide (CO) ina gas flow ratio of no less than approximately 0.104 and no greater thanapproximately 0.2; stripping the photoresist using a plasma chemistryincluding tetrafluoro methane (CF₄) using a gas flow of no less thanapproximately 7 standard cubic centimeters per minute (sccm) and nogreater than approximately 15 sccm of the tetrafluoro methane (CF₄); andetching the cap layer to open the via to the conductor usingapproximately 150 mT of pressure, an RF energy of approximately 1000 Wat 2 MHz and approximately 1500 W at 27 MHz, and a gas flow includingtetrafluoro methane (CF₄) and trifluoro methane (CHF₃) in a gas flowratio of no less than approximately 2.33 and no greater thanapproximately 3.96.

A fourth aspect of the invention relates to a method of etching a firstdielectric layer, a second dielectric layer and a cap layer over aconductor level to open a via to the conductor, a pattern for the viabeing provided by a photoresist, the method comprising the steps of:etching the via through the first dielectric layer; etching the viathrough the second dielectric layer; stripping the photoresist using aplasma chemistry including tetrafluoro methane (CF₄); and etching thecap layer to open the via to the conductor.

The foregoing and other features of the invention will be apparent fromthe following more particular description of embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of this invention will be described in detail, withreference to the following figures, wherein like designations denotelike elements, and wherein:

FIG. 1 shows a conventional semiconductor structure including large-viapad dielectric layers prior to etching.

FIGS. 2–5 show a method of etching a via according to the invention.

FIG. 6 shows a semiconductor structure illustrating some of the problemssolved by the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the accompanying drawings, FIGS. 2–5 show a method ofetching a dielectric layer and a cap layer over a conductor level toopen a via to the conductor according to the invention. The methodmodifies the conventional process such that the process results inimproved yields, more predictable etch rates and greatly reducedprocessing time. The process begins with a conventional semiconductorstructure 10 including large-via pad dielectric layers 12, similar tothat shown in FIG. 1. Structure 10 includes a conductor level 14including a dielectric layer 16 (e.g., of silicon dioxide SiO₂ or anyother appropriate dielectric material) surrounding conductor 18 (e.g.,of copper Cu); a cap layer 20 atop conductor level 14; a dielectriclayer 22; another dielectric layer 24 (e.g., of silicon nitride Si₃N₄ orany other dielectric material); and a patterned photoresist 26.Patterned photoresist 26 includes a pattern (opening) for the via to beformed. Dielectric layer 22 may include any silicon dioxide (SiO₂) typematerial such as hydrogenated silicon oxycarbide (SiCOH), CORAL™available from Novellus, tetraethyl orthosilicate (Si(OC₂H₅)₄)(TEOS),fluorine doped TEOS (FTEOS), fluorine doped silicate glass (FSG),undoped silicate glass (USG), boro-phospho-silicate glass (BPSG), etc.Cap layer 20 may include any typical cap material such as: high densityplasma (HDP) silicon nitride, ultraviolet light transparent siliconnitride (UVN), silicon carbide (SiC), etc.

An initial step of the method includes, as shown in FIG. 2, etchingthrough dielectric (e.g., silicon nitride) layer 24. Since the etchconditions 100 used may be any conventional method, this step is notconsidered an integral part of the invention in all cases.

Next, as shown in FIG. 3, the via is etched through dielectric layer 22.In one embodiment, etching recipe 104 includes using approximately 80mTorr (mT) of pressure, and an RF energy of approximately 1200 watts (W)at 27 MHz and approximately 2700 W at 2 MHz, which represents anincrease in RF energy compared to the conventional process. A gas flowfor this embodiment includes tetrafluoro methane (CF₄) and carbonmonoxide (CO) in a gas flow ratio of approximately 0.104–0.200, andpreferably about 0.136. Tetrafluoro methane (CF₄) (also known as carbontetrafluoride) is an etchant that etches practically all dielectrics,and is available, for example, under the brand name Freon® 14 fromDupont. In one embodiment, the gas flow includes approximately 25–40sccm of tetrafluoro methane (CF₄) (preferably about 30 sccm), andapproximately 200–240 sccm of carbon monoxide (CO) (preferably about 220sccm). In addition, the gas flow includes approximately 400 sccm ofargon (Ar). This etch recipe 102 provides more than twice as fast anetch rate (i.e., approximately 95 Ångstroms/second (Å/s)) as theconventional process due to an increased amount of tetrafluoro methane(CF₄). In addition, this etch recipe 102 is highly selective to caplayer 20, and causes no changes in the etch profile compared to theconventional process.

Referring to FIG. 4, a next step includes stripping the photoresistusing a plasma chemistry 102 including tetrafluoro methane (CF₄), whichis not used in conventional stripping processes. In one embodiment, thephotoresist stripping step includes two stages. A first stage usesapproximately 120 mT of pressure, and an RF energy of approximately 1000W at 27 MHz and approximately 200 W at 2 MHz. In one embodiment, a gasflow of approximately 900–1100 sccm of oxygen (O₂) (preferably about1000 sccm) is used in the first stage. A second stage uses approximately400 mT of pressure, and an RF energy of approximately 1600 W at 2 MHz. Agas flow of the second stage includes tetrafluoro methane (CF₄) andoxygen (O₂) in a gas flow ratio of approximately 0.006–0.016, andpreferably about 0.010. During the second stage, the tetrafluoro methane(CF₄) may be provided at approximately 7–15 sccm (preferably about 10sccm), and the oxygen (O₂) may be provided at approximately 900–1100sccm (preferably about 1000 sccm).

The photoresist strip step according to the invention adds tetrafluoromethane (CF₄) gas to remove photoresist polymer 134 (FIG. 6) left behindfrom the high RF energy used during the dielectric etching 100 (FIG. 3).Contrary to expectations, however, the addition of tetrafluoro methane(CF₄) does not etch cap layer 20 sufficiently to cause exposure ofconductor 18, and does not affect the etch profile. In particular, a lowgas flow and duration provides enough tetrafluoro methane (CF₄) toobtain a clean strip of the hardened photoresist polymer 134 (FIG. 6)while minimizing the etching of cap layer 20. More significantly,however, the addition of tetrafluoro methane (CF₄) cuts the etching timein approximately half compared to the conventional process, whichgreatly increases the overall speed of the via RIE process. Inparticular, this stage may last approximately 10–15 seconds, which issignificantly shorter than the conventional process, which typicallylasts 20–30 seconds. Another advantage of the tetrafluoro methane (CF₄)usage is that it removes residual polymer created by the oxygen (O₂)etch (FIG. 3), and leaves a clean cap layer 20 surface after photoresiststrip. As shown in FIG. 6, the oxygen (O₂) etch with such a high RFenergy tends leave photoresist 26 (FIG. 3) harder than in conventionalRIE processes, which causes increased residual photoresist polymer 134,e.g., carbon mixed with oxide. However, the tetrafluoro methane (CF₄)removes this residual polymer.

Referring to FIG. 5, the next step includes etching cap layer 20 to openthe via to conductor 18. In one embodiment, the cap layer etching stepincludes an etch recipe 106 using approximately 150 mT of pressure, andan RF energy of approximately 1000 W at 2 MHz and approximately 1500 Wat 27 MHz. A gas flow includes tetrafluoro methane (CF₄) and trifluoromethane (CHF₃) in a gas flow ratio of approximately 2.33–3.96. Trifluoromethane (CHF₃) (also known as fluoroform) is available, for example,under trade name Freon® 23 from Dupont. The addition of trifluoromethane (CHF₃) is presented in this step to improve sidewall profilestriations, which would lead to higher contact resistance. In oneembodiment, the gas flow includes approximately 80–110 sccm of oxygen(O₂) (preferably about 100 sccm), approximately 170–210 sccm of thetetrafluoro methane (CF₄) (preferably about 190 sccm), and approximately53–73 sccm of the trifluoro methane (CHF₃) (preferably about 63 sccm).The gas flow also includes approximately 400 sccm of argon (Ar).

With further regard to the cap layer etching step, for certain types ofvias, the thickness of cap layer 20 may be thicker than in other via paddielectric stacks. For instance, the above values are optimal for a caplayer 20 having a thickness of approximately 800–1200 Å, i.e., about1000 Å, of, for example, silicon nitride. However, thicker cap layers120 of, for example, silicon nitride, such as shown in FIG. 6, aresubject to undercutting 130 and metal oxidation 132 that lead to highercontact resistance when the above-described amount of oxygen (O₂) isused. To address this situation, in an alternative embodiment, the gasflow includes the same gases and rates as described above, except theamount of oxygen (O₂) is reduced by a factor of approximately 10, whichprevents the undercutting. In one embodiment, the amount of oxygen isapproximately 7–13 sccm, and is preferably about 10 sccm. This amount ofoxygen (O₂) has been found sufficient for cap layers 120 (FIG. 6) havinga thickness of approximately 2500–3500 Å, i.e., about 3000 Å, of, forexample, silicon nitride. In particular, the given oxygen gas flowresults in no lateral undercut 130 (FIG. 6), minimal metal oxidation 134(FIG. 6), and does not compromise etching time. Further decrease inoxygen gas, however, results in a dramatic drop in etch rate.

The above-described method also reduces processing time by eliminatingthe need for a nitrogen-hydrogen plasma chemistry (ash) step as inconventional via RIE processing. This saves approximately 45 seconds perwafer. The invention also attains required wall profile angle, provideshigh selectivity of dielectric layer 22 etching chemistry 104 to caplayer 20, and minimal oxidation of a surface of metal 18. The inventioncan be applied to any large via pads requiring high etching selectivityto a cap layer 20, minimal cap layer 20 undercutting, and reduced metaloxidation. The invention provides higher yield, more predictable etchrates, and faster processing, and removes the need for an ash step.

The following table summarizes the RIE etch parameters for a preferredembodiment:

Photo- Cap Layer Cap Dielectric Photoresist resist 20 Layer 120 Layer 22Stage 1 Stage 2 (~1000Å) (~3000Å) Pressure 80 120 400 150 150 (mT) RFenergy (W) 27 MHz 1200 1000 0 1500 1500  2 MHz 2700 200 1600 1000 1000Gas Flow (sccm) CH₄ 25–40 0 7–15 170–210 170–210 CHF₃ 0 0 0 53–73 53–73CO 200–240 0 0 0 0 O₂ 0 900–1100 900–  80–110  7–13 1100 Ar 400 0 0 400400 Gas Flow Ratios: CF₄/CO 0.104–0.200 — — — — CF₄/O₂ — — 0.006– — —0.0160 CF₄/CHF₃ — — — 2.33–3.96 2.33–3.96

While this invention has been described in conjunction with the specificembodiments outlined above, it is evident that many alternatives,modifications and variations will be apparent to those skilled in theart. Accordingly, the embodiments of the invention as set forth aboveare intended to be illustrative, not limiting. Various changes may bemade without departing from the spirit and scope of the invention asdefined in the following claims.

1. A method of etching a dielectric layer and a cap layer over aconductor level to open a via to a conductor, a pattern for the viabeing provided by a photoresist, the method comprising the steps of:etching the via through the dielectric layer; stripping the photoresistusing a plasma chemistry including tetrafluoro methane (CF₄); andetching the cap layer to open the via to the conductor; wherein thedielectric layer etching step includes using approximately 80 mT ofpressure, an RF energy of approximately 1200 W at 27 MHz andapproximately 2700 W at 2 MHz, and a gas flow including tetrafluoromethane (CF₄) and carbon monoxide (CO) in a gas flow ratio of no lessthan approximately 0.104 and no greater than approximately 0.2.
 2. Themethod of claim 1, wherein the gas flow during the dielectric layeretching step includes no less than approximately 25 and no greater thanapproximately 40 standard cubic centimeters per minute (sccm) oftetrafluoro methane (CF₄), no less than approximately 200 and no greaterthan approximately 240 sccm of carbon monoxide (CO), and approximately400 sccm of argon (Ar).
 3. The method of claim 1, wherein the dielectriclayer etching step has an etch rate of approximately 95 Ångstroms/second(Å/s).
 4. The method of claim 1, wherein the photoresist stripping stepincludes using a gas flow of no less than approximately 7 standard cubiccentimeters per minute (sccm) and no greater than approximately 15 sccmof the tetrafluoro methane (CF₄).
 5. A method of etching a dielectriclayer and a cap layer over a conductor level to open a via to aconductor, a pattern for the via being provided by a photoresist, themethod comprising the steps of: etching the via through the dielectriclayer; stripping the photoresist using a plasma chemistry includingtetrafluoro methane (CF₄); and etching the cap layer to open the via todie conductor; wherein the photoresist stripping step includes twostages including: a first stage using approximately 120 mT of pressure,an RF energy of approximately 1000 W at 27 MHz and approximately 200 Wat 2 MHz, and a gas flow including oxygen (O₂); and a second stage usingapproximately 400 mT of pressure, an RF energy of approximately 1600 Wat 2 MHz, and a gas flow including the tetrafluoro methane (CF₄) andoxygen (O₂) in a gas flow ratio no less than approximately 0.006 and nogreater than, approximately 0.016.
 6. The method of claim 5, wherein thegas flow of the first stage includes no less than approximately 900standard cubic centimeters per minute (sccm) and no greater thanapproximately 1100 sccm of the oxygen O₂.
 7. The method of claim 5,wherein the gas flow of the second stage includes no less thanapproximately 7 standard cubic centimeters per minute (sccm) and nogreater than approximately 15 sccm of the tetrafluoro methane (CF₄), andno less than approximately 900 sccm and no greater than approximately1100 sccm of the oxygen (O₂).
 8. The method of claim 5, wherein the caplayer etching step includes using approximately 150 mT of pressure, anRF energy of approximately 1000 W at 2 MHz and approximately 1500 W at27 MHz, and a gas flow including tetrafluoro methane (CF₄) and trifluoromethane (CHF₃) in a gas flow ratio of no less than approximately 2.33and no greater than approximately 3.96.
 9. The method of claim 8,wherein, in the case that the cap layer has a thickness of no less thanapproximately 800 Å and no greater than 1200 Å, the cap layer etchingstep gas flow includes no less than approximately 80 and no greater thanapproximately 110 standard cubic centimeters per minute (sccm) of oxygen(O₂), no less than approximately 170 and no greater than approximately210 sccm of tetrafluoro methane (CF₄), no less than approximately 53 andno greater than approximately 73 sccm of trifluoro methane (CHF₃), andapproximately 400 sccm of argon (Ar).
 10. The method of claim 8,wherein, in the case that the cap layer has a thickness of no less thanapproximately 2500 Å and no greater than 3500 Å, the cap layer etchingstep gas flow includes no less than approximately 7 and no greater thanapproximately 13 standard cubic centimeters per minute (sccm) of oxygen(O₂), no less than approximately 170 and no greater than approximately210 seem of tetrafluoro methane (CF₄), no less than approximately 53 andno greater than approximately 73 sccm of trifluoro methane (CHF₃), andapproximately 400 sccm of argon (Ar).
 11. A method of etching adielectric layer and a cap layer over a conductor level to open a via toa conductor, a pattern for the via being provided by a photoresist themethod consisting of the steps of: etching the via through thedielectric layer; stripping the photoresist using a plasma chemistryincluding tetrafluoro methane (CF₄); and etching the cap layer to openthe via to the conductor; wherein the dielectric layer etching stepincludes using approximately 80 mT of pressure, an RF energy ofapproximately 1200 W at 27 MHz and approximately 2700 W at 2 MHz, and agas flow including tetrafluoro methane (CF₄) and carbon monoxide (CO) ina gas flow ratio of no less than approximately 0.104 and no greater thanapproximately 0.2.
 12. The method of claim 11, wherein the gas flowduring the dielectric layer etching step includes no less thanapproximately 25 and no greater than approximately 40 standard cubiccentimeters per minute (sccm) of tetrafluoro methane (CF₄), no less thanapproximately 200 and no greater than approximately 240 sccm of carbonmonoxide (CO), and approximately 400 sccm of argon (Ar).
 13. The methodof claim 11, wherein the photoresist stripping step includes using a gasflow of no less than approximately 7 standard cubic centimeters perminute (sccm) and no greater than approximately 15 sccm of thetetrafluoro methane (CF₄).
 14. The method of claim 11, wherein thephotoresist stripping step includes two stages including: a first stageusing approximately 120 mT of pressure, an RE energy of approximately1000 W at 27 MHz and approximately 200 W at 2 MHz, and a gas flowincluding oxygen (O₂); and a second stage using approximately 400 mT ofpressure, an RF energy of approximately 1600 W at 2 MHz, and a gas flowincluding the tetrafluoro methane (CF₄) and oxygen (O₂) in a gas flowratio no less than approximately 0.006 and no greater than approximately0.016.
 15. The method of claim 14, wherein the gas flow of the firststage includes no less than approximately 900 standard cubic centimetersper minute (sccm) and no greater than approximately 1100 sccm of theoxygen (O₂).
 16. The method of claim 14, wherein the gas flow of thesecond stage includes no less than approximately 7 sccm and no greaterthan approximately 15 sccm of the tetrafluoro methane (CF₄), and no lessthan approximately 900 sccm and no greater than approximately 1100 sccmof the oxygen (O₂).
 17. The method of claim 11, wherein the cap layeretching step includes using approximately 150 mT of pressure, an RFenergy of approximately 1000 W at 2 MHz and approximately 1500 W at 27MHz, and a gas flow including tetrafluoro methane (CF₄) and trifluoromethane (CHF₃) in a gas flow ratio of no less than approximately 2.33and no greater than approximately 3.96.
 18. The method of claim 17,wherein, in the case that the cap layer has a thickness of no less thanapproximately 800 Å and no greater than 1200 Å, the cap layer etchingstep gas flow includes no less than approximately 80 and no greater thanapproximately 110 standard cubic centimeters per minute (sccm) of oxygen(O₂), no less than approximately 170 and no greater than approximately210 sccm of tetrafluoro methane (CF₄), no less than approximately 53 andno greater than approximately 73 sccm of trifluoro methane (CHF₃), andapproximately 400 sccm of argon (Ar).
 19. The method of claim 17,wherein, in the case that the cap layer has a thickness of no less thanapproximately 2500 Å and no greater than 3500 Å, the cap layer etchingstep gas flow includes no less than approximately 7 and no greater thanapproximately 13 standard cubic centimeters per minute (sccm) of oxygen(O₂), no less than approximately 170 and no greater than approximately210 sccm of tetrafluoro methane (CF₄), no less than approximately 53 andno greater than approximately 73 sccm of trifluoro methane (CHF₃), andapproximately 400 sccm of argon (Ar).
 20. A method of etching adielectric layer and a cap layer over a conductor level to open a via toa conductor, a pattern for the via being provided by a photoresist, themethod comprising of the steps of: etching the via through thedielectric layer using approximately 80 mT of pressure, an RF energy ofapproximately 1200 W at 27 MHz and approximately 2700 W at 2 MHz, and agas flow including tetrafluoro methane (CF₄) and carbon monoxide (CO) ina gas flow ratio of no less than approximately 0.104 and no greater thanapproximately 0.2; stripping the photoresist using a plasma chemistryincluding tetrafluoro methane (CF₄) using a gas flow of no less thanapproximately 7 standard cubic centimeters per minute (sccm) and nogreater than approximately 15 sccm of the tetrafluoro methane (CF₄); andetching the cap layer to open the via to the conductor usingapproximately 150 mT of pressure, an RF energy of approximately 1000 Wat 2 MHz and approximately 1500 W at 27 MHz, and a gas flow includingtetrafluoro methane (CF₄) and trifluoro methane (CHF₃) in a gas flowratio of no less than approximately 2.33 and no greater thanapproximately 3.96.
 21. The method of claim 20, wherein the gas flow thedielectric layer etching step includes no less than approximately 25 andno greater than approximately 40 standard cubic centimeters per minute(sccm) of tetrafluoro methane (CF₄), no less than approximately 200 andno greater than approximately 240 sccm of carbon monoxide (CO), andapproximately 400 sccm of argon (Ar).
 22. The method of claim 20,wherein die photoresist stripping step includes two stages including: afirst stage using approximately 120 mT of pressure, an RF energy ofapproximately 1000 W at 27 MHz and approximately 200 W at 2 MHz, and agas flow of no less than approximately 900 standard cubic centimetersper minute (sccm) and no greater than approximately 1100 seem of oxygen(O₂); and a second stage using approximately 400 mT of pressure, an RFenergy of approximately 1600 W at 2 MHz, and a gas flow including thetetrafluoro methane (CF₄) and oxygen (O₂) in a gas flow ratio no lessthan approximately 0.006 and no greater than approximately 0.016. 23.The method of claim 22, wherein the gas flow of the second stageincludes no less than approximately 900 sccm and no greater thanapproximately 1100 sccm of the oxygen (O₂).
 24. The method of claim 20,wherein, in the case that the cap layer has a thickness of no less thanapproximately 800 Å and no greater than 1200 Å, the cap layer etchingstep gas flow includes no less than approximately 80 and no greater thanapproximately 110 standard cubic centimeters per minute (sccm) of oxygen(O₂), no less than approximately 170 and no greater than approximately210 sccm of tetrafluoro methane (CF₄), no less than approximately 53 andno greater than approximately 73 sccm of trifluoro methane (CHF₃), andapproximately 400 sccm of argon (Ar).
 25. The method of claim 20,wherein, in the case that the cap layer has a thickness of no less thanapproximately 2500 Å and no greater than 3500 Å, the cap layer etchingstep gas flow includes no less than approximately 7 and no greater thanapproximately 13 standard cubic centimeters per minute (sccm) of oxygen(O₂), no less than approximately 170 and no greater than approximately210 sccm of tetrafluoro methane (CF₄), no less than approximately 53 andno greater than approximately 73 sccm of trifluoro methane (CHF₃), andapproximately 400 sccm of argon (Ar).